Context. Despite their carbon-rich photospheres, silicate carbon stars show 10 μm silicate emission. They are considered to have circumbinary or circum-companion disks, which serve as a reservoir of oxygen-rich material shed by mass loss in the past. Aims. We present N-band spectro-interferometric observations of the silicate carbon star BM Gem using MIDI at the Very Large Telescope Interferometer (VLTI). Our aim is to probe the spatial distribution of oxygen-rich dust at high spatial resolution. Methods. Using the UT2-UT3 and UT3-UT4 configurations, BM Gem was observed with VLTI/MIDI at 44-62 m baselines. Results. The N-band visibilities observed for BM Gem decrease steeply between 8 and ∼10 μm and increase gradually longward of ∼ 10 μm, reflecting the optically thin silicate emission feature emanating from sub-micron-sized amorphous silicate grains. The differential phases obtained at baselines of ∼44-46 m show significant non-zero values (∼-70°) in the central part of the silicate emission feature between ∼9 and 11 μm, revealing a photocenter shift and the asymmetric nature of the silicate emitting region. The observed N-band visibilities and differential phases can be described adequately by a simple geometrical model in which the unresolved star is surrounded by a ring with azimuthal brightness modulation. The best-fit model is characterized by a broad ring ∼70 mas across at 10 μm) with a bright region offset from the unresolved star by ∼20 mas at a position angle of ∼280°. This model can be interpreted as a system with a circum-companion disk and is consistent with the spectroscopic signatures of an accretion disk around an unseen companion, which were discovered in the violet spectrum of BM Gem.
Áreas temáticas de ASJC Scopus
- Astronomía y astrofísica
- Ciencias planetarias y espacial